This study was undertaken to seek evidence of natural selection with respect to human behavioral characteristics. The population chosen consisted of about 13,000 German-speaking Mennonites whose culture resembles in many respects that of pre-industrial European peasants. A census-survey was made in 1967 and vital records, kept by the church, were copied. The editing of these two types of record has been very time-consuming, and is still in progress. When editing is completed, relations will be explored between vital events and socio-economic variables. The principal hypothesis to be tested is that, under conditions of natural human reproduction, individual behavior that is economically successful results also in superior biological reproduction.